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Abstract

We studied the transient behaviors of current-injection quantum-dot microdisk lasers at room temperature. Unique optical responses were observed, including the suppression of relaxation oscillations and fast turn-on. With the help of rate-equation modeling, the suppressed relaxation oscillations are attributed to the enhanced spontaneous emission factor in microdisk lasers. Short turn-on time, around 1 ns without pre-bias, results from the reduced carrier lifetime caused by the Purcell effect and increased nonradiative recombination rate due to higher surface/volume ratio. With short turn-on time, a large-signal direct modulation experiment at 1 Gbps is demonstrated. Modal transient behavior was also investigated under various temperatures from 100 to 300 K. Both of the transient lasing and steady-state lasing from side modes are suppressed at temperatures higher than 250K. Therefore, the quantum-dot microdisk lasers show the potential of single-mode operation under high-speed modulation at room temperature.

The temporal optical responses measured from (a) a QD microdisk laser and (b) a conventional QD edge-emitting laser fabricated from the same wafer. The origins of time axis are defined by the rising edge of the electric pulses. The normalized injection currents are indicated in the graphs.

The temporal optical responses calculated from the rate-equation model for (a) a QD microdisk laser and (b) a conventional QD edge-emitting laser. The injection starts at t = 0 ns. The normalized injection currents are indicated in the graphs.

(a) The observed WGM wavelengths of a 6.5-μm-diamenter microdisk laser at different temperatures. (b)-(d): The temporal optical responses measured at (b) 100 K, (c) 150 K, and (d) 200 K. For 250 K and 300 K, there is only one WGM lasing with the temporal response similar to those in Fig. 3(a).